A Study of the North Water Polynya Ice Arch using Four Decades of Satellite Data

R F Vincent

doi:10.1038/s41598-019-56780-6

Abstract

Polynyas are sections of the polar ocean that remain relatively ice-free during winter, imparting significant physical and biological impact on the region. The North Water polynya (NOW) situated between Ellesmere Island and Greenland is the largest recurring Arctic polynya. Historically, the NOW forms every season when Arctic Ocean floes moving southward through Nares Strait become congested and form an ice arch that defines the northern border of the polynya. This blockage usually forms during winter and breaks down in spring. It is conjectured that the polynya is maintained by latent heat of fusion from the continuous formation of new ice as floes are swept southward from the ice arch by wind and ocean currents. Analysis of four decades of satellite imagery indicates a growing instability in the location of the ice arch, challenging previous models of polynya maintenance. A linear trend of the data indicates the number of days of Nares Strait blockage has decreased 2.1 days/year between 1979 and 2019 with wide interannual variations. Prior to 2007, ice arches blocked Nares Strait an average of 177 days/year compared to 128 days/year since that time. The overall trend of reduced ice arch duration is a contributing factor to the dramatic loss of multiyear ice in the Arctic basin.

Highlights

Polynyas are areas of the polar ocean that are covered by open-water and thin ice under climatic conditions that would normally dictate thick ice cover
While the Smith Sound ice arch sharply defines the northern limit of the polynya (Fig. 1b), the southern boundary is characterized by diffuse pack ice in northern Baffin Bay
The formation and duration of ice arches in the Nares Strait system impacts the rate of ice loss from this reservoir, which is part of a region that climate models predict will be the last to lose perennial ice cover in the Arctic Ocean known as the Last Ice Area[33]

Summary

Introduction

Polynyas are areas of the polar ocean that are covered by open-water and thin ice under climatic conditions that would normally dictate thick ice cover These regions are generally classified as latent or sensible heat polynyas. Pack ice transported southward from the Arctic Ocean through Nares Strait becomes congested and forms a blockage, or ice arch, across the narrow head of Smith Sound. The Smith Sound ice arch usually forms in winter or early spring at which point ice is continuously swept southward from the blockage by prevailing winds and ocean currents[21,22,23]. The Smith Sound ice arch usually breaks down in June or July at which point the polynya is indiscernible as ice floes from the Arctic Ocean enter the area through Nares Strait. The consistency of the Smith Sound ice arch from 1968 to 1979 is illustrated by ice charts created during this era in which it averages a seasonal latitude of 79.2 ± 0.5°N. (Fig. 2)

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